1. Field of the Invention
The invention relates to a system for transferring energy to a vehicle, in particular a track bound vehicle, such as a light rail vehicle. In particular, the light rail vehicle may be a tram. The invention further relates to a method of operating such a system and it relates to a method of manufacturing such a system.
2. Description of Related Art
Trams are usually provided with electric energy via a pantograph which contacts a conductor like an overhead line or a live rail. However, under specific circumstances such as within the historic centre of a city such conductors are undesired for aesthetic reasons. On the other hand, live rails which are buried in the ground cause safety problems.
To overcome this problem, energy can be transferred inductively to the vehicle. A track side conductor arrangement produces an electromagnetic field. The field is received by a coil on board of the vehicle so that the field produces an electric voltage by induction. The transferred energy may be used for propulsion of the vehicle and/or for other purposes such as providing auxiliary systems of the vehicle (e.g. the heating and ventilating system) with energy.
The system for transferring the energy to the vehicle which comprises the electric conductor arrangement may also comprise electric and/or electronic devices which are adapted to operate the electric conductor arrangement. One of the devices may be an inverter for generating an alternating current from a direct current. The direct current may be carried by a supply line which supplies electric energy to the conductor arrangement. The alternating current may be the current which is carried by the conductor arrangement to produce the electromagnetic field. Since comparatively high powers are required by the vehicle, a corresponding power inverter produces significant losses in form of heat power. However, the electric and/or electronic device for operation of the electric conductor arrangement may comprise other types of devices, such as power switches to switch on and off a section of the electric conductor arrangement, detection devices for detecting the presence of a vehicle and other devices.
These devices can be arranged in boxes or other casings above ground. Therefore, the heat losses produced by the devices can easily be transferred to the ambience. However, this may result in unacceptable noise production if ventilators are used to force the cooling. Furthermore, especially within historic parts of cities, casings above ground are not acceptable. On the other hand, burying the devices in the ground deteriorates the heat transfer to the ambience. Typical ground materials such as soil, rocks and sand are poor heat conductors.
It is an option to bury the devices directly in the ground. DE 699 29 353 T2 discloses to bury a transformer directly in the ground, wherein the primary and secondary winding of the transformer are cast in an insulating material, whereas the magnetic core of the transformer is uncovered in order to transfer heat to the surrounding soil. However, directly burying the devices for operating the conductor arrangement makes it difficult to perform maintenance of the devices and replacement of parts, if necessary. Furthermore, especially electronic devices such as semiconductor switches would require at least some kind of protection against water and dirt. In addition, the thermal conductivity of natural ground materials is small and the heat is therefore badly removed from the transformer.